The invention relates to an apparatus for inserting chipboard or cardboard spacers at regular intervals between paper sheets being fed by a press onto a lapstream conveyor for making writing tablets or the like.
The insertion of chipboard or cardboard spacers in a stream of paper sheets on a lapstream conveyor issuing from a press without slowing or stopping the press and/or conveyor has long presented a problem within the industry. The term "lapstream" refers to the manner in which the sheets are arranged on the conveyor in an overlapped stream.
Many prior inserting devices have placed chipboard spacers after the paper sheets have been deposited in a vertical stack at the end of the conveyor. This has necessitated the insertion of a mechanical finger at appropriate points in the paper stack to lift the topmost sheets while a chipboard ejector injects a chipboard spacer under the mechanical finger. Such an operation can result in damage to the paper sheets by the mechanical finger or the chipboard injector and precise positioning of the mechanical finger in the stack is difficult. This can result in differing numbers of sheets in the tablets.
A different approach for relatively small production facilities has been to divert a plurality of sheets from the continuous lapstream to mark a point at which a chipboard spacer is to be inserted. This is a time consuming process which requires an operator to physically pick up the paper bundles between diversions and put the spacers in place. It is not suitable for large, high speed presses.
Yet another approach has been to insert chipboard spacers into a vertical stack as the paper sheets are being fed to the stack. Generally, the flow of sheets to the stack has been temporarily interrupted while the spacers are inserted, thus resulting in lost production time and inefficiency.
Prior art attempts to interleave chipboard spacers or covers within paper sheets on a lapstream conveyor belt before they are vertically stacked have generally included parallel feeders where the paper sheets and the spacers are on parallel tracks and are fed into the lapstream from the same direction. In such parallel operations, complex and precisely timed counters, rollers and injectors have been required, resulting in machines which are difficult to synchronize and maintain. Any imprecision in timing between the parallel feeders can result in machine jams and consequent down time and productivity loss. Furthermore, it has been impossible to add a parallel chipboard spacer inserter to an existing conveyor, i.e. such inserters must necessarily be integrated into the lapstream conveyor when it is manufactured.
It is clear then, that a relatively simple and inexpensive chipboard inserter which efficiently and reliably inserts chipboard spacers at precise points within a paper sheet lapstream is needed. It is also clear that such an inserter should be capable of being added to an existing lapstream conveyor and that it should work without requiring the press and/or the lapstream conveyor to be slowed or stopped. Such an inserter should be capable of automatic operation so that a single operator can supervise a plurality of inserters in a modern, high-speed printing shop.